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A method was developed for performing strain-controlled fatigue tests on steel specimens with thickness <0.1 inch. Data generated using this method were found to be consistent with published results for steels of similar strength and thickness. Geometric variables, i.e., gage section width and area, gage length, etc., have little effect on valid fatigue results (excluding buckling, excessive bending, and out-of-gage length failures). However, increased gage length or specimen width increase the likelihood of invalid results.

Variability in published strain-cycle fatigue data was essentially independent of grade and strain amplitude for life <2×106 reversals. Correlations between tensile properties and strain-cycle fatigue parameters were either not statistically significant or so highly variable as to be of doubtful practical importance. However, for a life of 2×106 reversals, total strain amplitude Δɛ/2 bore a significant relation to tensile strength σu. Present findings emphasize the need for caution in estimating life when data are unavailable since such estimates encompassed a range in life 10 to 100 times greater than was actually observed.

The effect of steel grade on reversals to crack Initiation in notched specimens 2Ni essentially reflected differences in tensile strength. The higher strength grades (B80RK,RQC100) required a greater value of the notch parameter KfΔS for a given 2Ni than the lower strength grades (1020,A36,B40PO). Stress ratio R had a significant effect on 2Ni with 2Ni increasing as R decreased from 0 to -1. The various predictive models studied (local strain, nominal stress, empirical) gave similar results in terms of the variability in estimates of 2Ni and the relation between the predicted and observed values.